Lecture 8

Extrasolar planets detection methods and strategy

Techniques

• Radial velocity• Transit• Astrometry• Microlensing• Direct

~ 530 planets to date:

Planets

Brown Dwarfs

Space-based photometry is more precise than ground-based

David Bennett

Radial Velocity—1 m/s

Marc Kuchner

1-5 yrs 5-10 yrs 10-15 yrs

Exoplanet Task Force 2008: A two-pronged strategy

M dwarfs

F, G, K dwarfs

Fast-track ground-based, and existing space assets

Requires technology investments And new space-based facilities

1-5 yrs 6-10 yrs 11-15 yrs

,masses, addresses Density, Characterize

M d

war

fsF,

G,

K d

war

fs

Characterize for habitability

Radial velocity Space Astrometry

If is > 0.1 and Exozodi < 10 Zodi

RV + Transit surveys+SIRTF JWST

Corot / Kepler Space Microlensing Space Direct Imaging

@< 1 AU @ 1-10AU

Techn development & exo-Zodi for direct detection missions

Why obtain the mass of a planet?

Densities of the planets

Mercury 5.43 (water = 1 g/cc)

Venus 5.25

Earth 5.52

Jupiter 1.33

Saturn 0.71

Moon/Europa 3.0

Icy Moons 1-2.

Ice = 0.9-1.Slicates=2-4Iron=7-8

Ideal regim

e

Degenerate regime

R

M

Rmax

“Normal” matter with finite compressibility (Coulomb interactions) and thermal presssure

Pressure is only increased by the mass of the particles which increases gravity, thus pulling the particles closer together. Mass increases the pressure is increased, and the particles become spaced closer together.

Zapolsky and Salpeter

Swift et al., Exoplanets (ed Seager, UA Press)

• For radial velocity detections in multiple planet systems, an upper limit to the masses of the bodies is obtained by dynamical stability arguments.

Raw data from Kepler 11. Colored dots correspond to planets. (a) is raw, and (b) processed.

Lissauer et al Nature 2011

Transit timing variations masses

Lissauer et al Nature 2011

Kepler 11 system

Do we really need the mass if we can directly image the planet?

Consider the radius(R) –albedo(A) ambiguity:

Reflected (optical) brightness goes as A R2

Infrared emission goes as (1-A) R2

With one or the other we cannot determine the radius. Need two missions or the ability to spatially resolve the disk.

It is doubtful that we will fly two direct imaging missions or one that can resolve the disk in any reasonable planning horizon.

Color concept (Traub): Broadband colors for each of the solar system’s planets are distinct—diagnose terrestrial vs gas giant? But: “There are more kinds of Earths in the heavens, Horatio, than are dreamt of in your philosophy...”

1-5 yrs 6-10 yrs 11-15 yrs

,masses, addresses Density, Characterize

M d

war

fsF,

G,

K d

war

fs

Characterize for habitability

Radial velocity Hi-precision RV

If is > 0.1 and Exozodi < 10 Zodi

RV + Transit surveys+SIRTF JWST

Corot / Kepler Microlensing Space Direct Imaging

@< 1 AU @ 1-10AU

Techn development & exo-Zodi for direct detection missions

Radial Velocity—0.1 m/s

Radial Velocity—1 m/s

General consensus of the experts here is that 10 cm/s is instrumentally achievable but there may be only a small number of G dwarfs sufficiently quiet to take advantage of this capability

= 0.05 but completeness falls off dramatically for >0.1 AU

Borucki et al. 2011

Conclusions• Mass is an essential parameter in addition to radius.

Strategies should not be designed around direct detection spectrometry/photometry only.

• RV may be the primary technique for finding masses of Earth-like bodies in nearby systems. Because the number of systems will be small, statistics cannot be used to constrain sine (orbit inclination), hence derived planet masses and densities will be lower limits.

• It is unclear right now whether Earth mass bodies in the Habitable Zone are sufficiently common for the “cheap TPF” strategy to apply. May need space-based microlensing to sort this out. NASA and ESA need to cooperate on this.